Irrigators can save money and water

April 01, 2002 12:00 am

A 2001 field trip introduced irrigators to the AgriMet station. Accessible via the Internet, the devices help irrigators decide how much water to apply. (Baker City Herald photograph by S. John Collins).

By MIKE FERGUSON

Of the Baker City Herald

With a few keystrokes on their home computer, area irrigators can obtain weather data this summer that will tell them exactly when to water next.

By applying a simple formula, producers can chart an irrigating course for the entire growing season guaranteed not only to save precious water, but money on their pumping costs as well.

Studies show that applying just the right amount of water will also improve crop yield, while over-watering actually reduces yield.

Those are the claims made by Peter Palmer, who runs the Northwest AgriMet program for the Bureau of Reclamation, and John Busch, Basin Engineer for the Natural Resources Conservation Service in Baker City. The two teamed up last week to put on a seminar designed to help irrigators feel more comfortable accessing and applying the data they need to make wise water use decisions.

Using AgriMet stations

Palmer focused on the data available from 55 remote agricultural weather stations he manages in six states. Like the other stations, the Baker Valley station, installed in 2001 on a Blatchford potato field, monitors air temperature; solar radiation; relative humidity; wind speed, direction and peak gust; and precipitation.

Those factors determine the evapotranspiration figure, or ET, the amount of water lost each day to the atmosphere by direct evaporation from soil and plant surfaces plus the transpiration from within the plant.

The ET is available on Palmers website, www.pn.usbr.gov/agrimet.

The number is updated daily on the website; it climbs on hot, windy days, but can fall dramatically even in August with a short stretch of relatively cool, calm weather.

The ET can help determine when to water, instead of the old fashioned way of determining when to water, which is the feel and appearance method of judging soil moisture (conveniently outlined in an NRCS brochure available locally).

How calculation works

Alfalfa is the benchmark crop, but most other crops grown locally are included on Palmers list.

Heres how the calculation for a typical irrigator would work:

Say youre growing potatoes in Powval Silt Loam. Your irrigation system uses a center pivot, so 84 percent of the water you apply reaches its intended destination.

Potatoes have a 24-inch root zone; watering any deeper than that is wasteful and it leaches the soil.

Multiply the root zone, 24, by the potato plants available water capacity, which is .21 inches, to get 5.04.

Multiply that number by .30, the maximum allowable depletion for potatoes, to get 1.5 inches, which is the total allowable depletion.

That number is important. Its how much water would give the grower a full soil profile, and well use it as our starting point to outline our mythical irrigation schedule.

Say its early August, and the ET for potatoes on Aug. 1 is .22 inches (that in fact was the actual number in Baker Valley Aug. 1, 2001). That number is subtracted from 1.5 to get 1.28.

Chart the ET for the next several days and keep subtracting, and by Aug. 6 of 2001 you would have been down to .01 inches of water available. It would have been time to irrigate the day before that, Palmer said sooner depending on how fast your system puts water where you need it.

An agriculture consultant Palmer knows said irrigators have saved between 15 and 50 percent on both water and power costs using ET data. Depending on the cost of power, he said, irrigating scientifically can save about $9 per acre in pumping costs alone.

In the Willamette Valley, when you throw in fertilizer loss (from over-watering), its saving people about $100 an acre, he said.

Minimizing risk

Irrigators are almost by definition risk averse people, Busch said. The new method allows them to take even fewer risks, by sticking to a schedule thats dictated solely by local weather conditions.

He said his experience working with irrigators has taught him three lessons:

o Without scientific tools, its impossible to know when to irrigate or how much water to apply.

o Errors in timing ones applications can be very expensive.

o Its important to use both soil and moisture measurements and computer models of evapotranspiration to keep track of soil moisture.

On the Web

The website has a more urban application as well. One column lists ET for lawn irrigation. With automatic sprinklers, city residents could water their lawn exactly when it needs it without even setting foot outside.